Well, put simply, biology is the study of life. Everything living is organic (everything living decomposes). Biologists study living things which have organic chemistry.
If DNA is found at a crime scene it can help locate people that were at the crime scene. If the criminal has committed crimes before their DNA will already be in the police system. If not they can take samples from suspects and pinpoint who committed the crime.
C) voltage gated sodium channels
have a great day!